Field of the Invention
The present invention relates to devices for converting chemical energy into electric energy. More particularly, the invention is concerned with sealed lead-acid storage batteries. The invention may be used as a self-contained source of electric energy in radioelectronics, transport means, etc. The invention is of particular advantage in the field of radioelectronics, especially when great temperature variations and low temperatures are involved.
With the development of engineering the demand for self-contained sources of electric energy in particular, for storage batteries increases. If at the beginning of this century the ship building and automobile construction industries were the main consumers of storage batteries, nowadays it is difficult to find a field of engineering where said devices are not employed. Storage batteries which are most extensively used at present in radioelectronics, communications engineering, aviation and medicine are alkaline batteries since they can be made hermetically sealed. But the alkaline storage batteries, as compared to the lead-acid batteries, have considerable disadvantages: a high cost and a low reliability in operation at high densities of currents (e.g. when used for starting engines) and at low ambient temperatures. The main disadvantage of the lead-acid storage batteries, which are cheaper as compared to the alkaline ones, is that up to now they could not be made hermetically sealed.
This disadvantage results from the fact that the lead-acid stoage batteries known in the art do not ensure a full absorption of the gases (oxygen and hydrogen) which evolve during their charging.
Non-hermetic storage batteries are rather inconvenient in operation because they may not be turned over, and the evolving acid vapours affect the neighbouring devices. Moreover, the electrolyte must be refilled and corrected. In radioelectronic equipment this type of storage batteries cannot be used at all.
In the known lead-acid storage battery described in French Pat. No. 2,290,048, gas evolution in the processes of charging is reduced by making the negative electrodes with a higher capacitance. In this case charging is carried out in stages and takes too much time, which complicates its operation. Moreover, this design does not fully eliminate gas evolution during the charging process, which is why a safety valve must be fitted in its upper wall. The need to use the safety valve and stages charging considerably complicates the storage battery design and its service, thus limiting the field of its application.
As compared to the above-described storage battery, gas evolution which occurs during the process of charging is considerably decreased in a storage battery (cf. Japanese Pat. No. 7038, N. Cl. 57, p. 145, 1969), wherein apart from the container, anode and cathode, there to provided an additional gas absorbing electrode. This gas absorbing electrode is made of a porous carbonaceous material soaked with the salts of such metals as platinum, palladium or ruthenium which are used as catalysts for the recombination reaction of the evolving gases, resulting in the formation of water. The auxiliary gas absorbing electrode is immersed in the electrolyte or placed on its surface and is positioned between the storage battery cathode and anode. The electrolyte is a mixture of sulphuric and phosphoric acids into which a thickening agent may be introduced such as, for example, liquid glass (SiO.sub.2) or pection. Charging of this storage battery is also carried out in two stages and takes dozens of hours. In the storage battery described above there is no gas evolution only in the initial stage of its operation. In the course of time the gas absorbing electrode catalyst becomes aged, its activity lowers, and the gas evolving during charging of the storage battery is not fully absorbed. Therefore this battery is also provided with a safety valve, which limits its application. In the case of using a liquid electrolyte the storage battery must be positioned with the valve upwards. In the case of a solidified electrolyte the storage battery internal resistance is higher and the storage batteries with solidified electrolytes do not operate sufficiently good when the ambient temperature greatly varies or is low. Moreover, the additional gas absorbing electrodes contain salts of precious metals as catalysts, which considerably increases the storage battery cost.